Manufacturing Process
Hand lay up / spray upu
Hand Lay Up / Spray Layup

Hand layup is an open contact molding in one-sided molds are the lowest-cost and most common processes for making fiberglass composite products and is the most common method of producing composites parts in the U.S. aircraft industry.

In a typical open mold application, the mold is first waxed and sprayed with gel coat. It then may be cured in a heated oven at about 120º F. In the spray-up process, after the gel coat cures, catalyzed resin (usually polyester or vinyl ester at 500 cps to 1000 cps viscosity) is sprayed into the mold, along with chopped fiberglass. A chopper gun chops roving (usually E-glass) directly into the resin spray, so that all materials are simultaneously applied to the mold. Using low-styrene and suppressed-styrene resins, fillers and high-volume/low-pressure spray guns or pressure-fed resin roller applicators helps reduce emissions of volatile organic compounds.

In hand lay-up processing, fiberglass (typically E-glass) continuous strand mat and/or other fabrics such as woven roving are manually placed in the mold. Each ply is sprayed with Catalyzed resin (1000 to 1500 cps) and the resin is worked into the fiber with brushes and rollers to wet-out and compact the laminate.

Fiber content can be increased by up to 50 percent by curing the part in a vacuum bag, using 2 psi to 14 psi vacuum pressure and cure temperatures under 350º F. Vacuum-assisted resin transfer molding (VARTM) and infusion molding systems are gaining favor with open-mold processors wanting to cut volatile organic compounds emissions. The applied vacuum compacts the preform and helps the resin to penetrate and wet-out the fiber preform. Fiber content up to 70 percent has been reported.

image from
by Charles A. Harper, 2000

Phenolic Liquid Resin Hand Lay-Up Techniques
Those fabricators making the transition from conventional ester and epoxy resins to phenolics who are already experienced in hand lay-up of structural reinforced plastics.

Materials Options:
Resins: Any, e.g. epoxy, polyester, vinylester, phenolic.
Fibers: Any. woven or stitched into a fabric form.
Cores: Any
Typical Applications:
most of aircraft composite parts, boat hulls and decks, RV components, truck cabs and fenders, wind-turbine blades etc.
Spray layup

Spray-up is an open-molding composites fabrication process where resin and reinforcements are sprayed onto a mold. The resin and glass may be applied separately or simultaneously "chopped" in a combined stream from a chopper gun. Workers roll out the spray-up to compact the laminate. Wood, foam or other core material may then be added, and a secondary spray-up layer imbeds the core between the laminates (sandwich construction). The part is then cured, cooled and removed from the reusable mold.

Spray layup has very little application in aerospace. This technology produces low specific strength structures which usually do not belong on the end product. Spray layup is being used to join back-up structures to composite face sheets on composite tools. Spray layup is also in limited use for obtaining fiberglass splash from transfer tools.

Related book
by Charles A. Harper, 2000

Phenolic Liquid Resin Hand Lay-Up Techniques

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